Attachments for tracking handheld implements

ABSTRACT

Devices and systems are provided for tracking a position and orientation of a handheld implement, such that the handheld implement may be trackable with an overhead tracking system. A support member secures one or more markers relative to a longitudinal portion of the handheld implement, and a marker plane containing the markers is orientated an angle relative to a longitudinal axis of the longitudinal portion. A marker assembly may include a support member for supporting the markers, and a connector for removably attaching the marker assembly to one or more handheld implements. The marker assembly may be configured to be removably attachable to a plurality of connection adapters, where each connection adapter is further connectable to a handheld implement, optionally at a calibrated position, such that a single connection adapter can be optionally employed to track a plurality of handheld implements. The handheld implement may be a medical instrument.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a National Phase application claiming the benefit ofPCT/CA2013/050512 filed on Jul. 3, 2013 in English, which further claimspriority to U.S. Provisional Application No. 61/667,714, titled“ATTACHMENTS FOR TRACKING HANDHELD IMPLEMENTS” and filed on Jul. 3,2012, the entire contents of which are incorporated herein by reference.

BACKGROUND

The present disclosure relates to guidance and tracking systems fortracking handheld implements, such as medical instruments. Moreparticularly, the present disclosure relates to active and passivemarker arrangements for surgical guidance and tracking of medicalinstruments.

Surgical guidance enables surgeons to localize the position of surgicalinstruments relative to the human body without having full visual accessduring surgery. Surgical guidance is routinely used in surgeries of thespine, brain, hip or other organs.

In general, surgical guidance consists of two steps: The first stepincludes the acquisition of a three dimensional (3D) representation ofrelevant portion of the body. This step may involve a single or multipleimaging modalities such as computer tomography (CT), magnetic resonancetomography (MRT), positron emission tomography (PET) and ultrasound(US). The 3D representation may be acquired before and/or during thesurgical procedure. In the second step, the spatial position of the bodyand the spatial relation of the surgical instruments to the position ofthe body are tracked during the surgery. The spatial position of thebody is correlated to its 3D representation using specific imageregistration techniques. After registration, the spatial position of thesurgical instruments can be displayed with a 3D representation of thebody for the surgeon.

Typically, optical-based systems are used for the tracking of thespatial positions during the surgery. These systems are based on twocameras that detect the positions of at least three markers attached tothe tracked surgical instruments (for example, mounted with LEDs asdisclosed in U.S. Pat. No. 5,921,992, or mounted with reflective probesas disclosed in U.S. Pat. No. 6,061,644).

There are many possible designs for the attachment of these markers tosurgical instruments that include a longitudinal shaft (for example,U.S. Pat. Nos. 6,021,343, 7,226,456 B2, 6,556,857 B1, 7,166,114 B2, andUS Patent No. 2002/0077540 A1). However, most of these designs include acommon characteristic that the cameras of the optical tracking systemare oriented to view the side of the shaft of the surgical instruments.The markers are therefore aligned along the instrument shaft.

In other applications, the tracking system may be oriented directlyabove the surgical incision, such that the tracking system “looks” intothe incision. These applications include arrangements for which thetracking system is integrated into the surgical lighting system (forexample, U.S. Pat. No. 7,224,472), or arrangements for which thetracking system is integrated into a system for performing opticaltopology imaging of anatomy within the incision (for example, U.S. Pat.Nos. 5,531,520 and 5,999,840 and PCT Patent ApplicationPCT/CA2011/050257).

SUMMARY

Devices and systems are provided for tracking a position and orientationof a handheld implement, such that the handheld implement may betrackable with an overhead tracking system. A support member secures oneor more markers relative to a longitudinal portion of the handheldimplement, and a marker plane containing the markers is orientated anangle relative to a longitudinal axis of the longitudinal portion. Amarker assembly may include a support member for supporting the markers,and a connector for removably attaching the marker assembly to one ormore handheld implements. The marker assembly may be configured to beremovably attachable to a plurality of connection adapters, where eachconnection adapter is further connectable to a handheld implement,optionally at a calibrated position, such that a single connectionadapter can be optionally employed to track a plurality of handheldimplements. The handheld implement may be a medical instrument.

Accordingly, in a first aspect, there is a marker assembly for locatinga handheld implement, the marker assembly comprising: a support member;at one or more tracking markers affixed to the support member, thetracking markers defining a marker plane; and a connector configured toremovably attach the support member to a longitudinal portion of thehandheld implement, the longitudinal portion defining a longitudinalaxis; wherein the marker plane is not parallel to the longitudinal axiswhen the marker assembly is secured to the handheld implement; andwherein the one or more tracking markers are suitable for locating athree-dimensional position and orientation of the handheld implementwhen the marker assembly is secured to the handheld implement.

In another aspect, there is provided an interchangeable marker systemfor tracking a plurality of handheld implements, the system comprising:a plurality of connection adapters, wherein each connection adapter isattached to, or attachable to, a longitudinal shaft of one of thehandheld implements, and wherein the connection adapters have a commonouter cross-section; and a marker assembly comprising: a longitudinalbody having an inner bore suitable for receiving one of the connectionadapters; a connection mechanism for connecting the longitudinal body tothe connection adapter; a support member connected to the longitudinalbody; and one or more tracking markers affixed to the support member,the tracking markers defining a marker plane; wherein the markerassembly is removably attachable to each of the handheld implementsthrough the connection adapters; and wherein the one or more trackingmarkers are suitable for locating a three-dimensional position andorientation of the handheld implement when the marker assembly issecured to the handheld implement.

In another aspect, there is provided a guidance system for tracking oneor more handheld implements, the guidance system comprising: a markerassembly as described above; a tracking system configured to detect asignal associated with each tracking marker, wherein the tracking systemis positioned in a substantially overhead configuration; and a processorconfigured to receive the signals and to calculate a relative positionand orientation of the handheld implement based on the signals, when themarker assembly is secured to the handheld implement.

In another aspect, there is provided a trackable handheld devicecomprising: a handheld implement comprising a longitudinal shaft, thelongitudinal shaft defining a longitudinal axis; a support memberconnected to the longitudinal shaft; and one or more tracking markersaffixed to the support member, the tracking markers defining a markerplane; wherein the marker plane is not parallel to the longitudinalaxis, such that the tracking markers are visible to an overhead trackingsystem during use of the handheld implement; and wherein the one or moretracking markers are suitable for locating a three-dimensional positionand orientation of the handheld implement by the overhead trackingsystem.

In another aspect, there is provided a trackable tool system comprising:a plurality of exchangeable tool extensions, each exchangeable toolextension having a proximal portion, a distal functional end, and alongitudinal axis; a handheld body adapted to detachably secure eachexchangeable tool extension at the proximal portion thereof, such thatone exchangeable tool extension may be secured to the handheld body atany given time; a support member connected to the handheld body; and oneor more tracking markers affixed to the support member, the trackingmarkers defining a marker plane; wherein each exchangeable toolextension has common length, such that when a first exchangeable toolextension is replaced with a second exchangeable tool extension, the oneor more tracking markers are suitable for locating a three-dimensionalposition of the distal functional end of the second exchangeable toolextension and an orientation the second exchangeable tool extension by atracking system without recalibration.

In another aspect, there is provided a guidance system for tracking oneor more handheld implements, the guidance system comprising: a trackablehandheld device as described above; a tracking system configured todetect a signal associated with each tracking marker, wherein thetracking system is positioned in a substantially overhead configuration;and a processor configured to receive the signals and to calculate arelative position and orientation of the handheld implement based on thesignals, when the support member is secured to the handheld implement.

In another aspect, there is provided a guidance system for tracking oneor more handheld implements, the guidance system comprising: aninterchangeable marker system as described above; a tracking systemconfigured to detect a signal associated with each tracking marker,wherein the tracking system is positioned in a substantially overheadconfiguration; and a processor configured to receive the signals and tocalculate a relative position and orientation of the handheld implementbased on the signals, when the marker assembly is secured to thehandheld implement.

A further understanding of the functional and advantageous aspects ofthe disclosure can be realized by reference to the following detaileddescription and drawings.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments will now be described, by way of example only, withreference to the drawings, in which:

FIG. 1 shows (a) a schematic of an example surgical guidance system thatincludes an overhead integrated tracking system that employs structuredlight surface detection for image registration and optical tracking ofmedical instruments and medical devices with marker attachments, (b) aconventional marker arrangement on a medical instrument for opticaltracking from the side direction, and (c) an illustration of the line ofsight obstruction problem that would occur with such an arrangement whenemployed with overhead tracking.

FIG. 2 provides (a) an example surgical guidance system that includes anoverhead integrated tracking system employing structured light surfacedetection for image registration and optical tracking of medicalinstruments and medical devices with marker attachments, where themarkers are attached to the medical instrument in a plane that is notparallel to a longitudinal axis of the medical instrument, as furthershown in (b) where full line of sight visibility of the markers isapparent.

FIG. 3 provides an isometric view of an example marker assemblyconnected to a medical instrument.

FIG. 4 is side view of the example marker assembly attached to themedical instrument, demonstrating the angle between the marker plane andthe shaft of the medical instrument.

FIG. 5 provides (a) a view of the example marker assembly attached tothe medical instrument, where the view is directed downward along theshaft of the medical instrument, such that the distal tip of the medicalinstrument is visible. (b) shows an illustration of the surgeon's pointof view of the optically tracked surgical instrument for medicalimplants.

FIG. 6 shows (a) an example marker assembly based on a hinge joint,which allows the user to select any arbitrary angle between theconnector and the marker arrangement, and (b) a detailed view of theindividual components of the hinge joint.

FIG. 7 illustrates the possible angle settings using the hinge jointbetween the connector and the marker arrangement as shown in FIG. 6.

FIG. 8 shows (a) an example marker assembly based on a hinge joint withnotches and a spring which allows the user to select an angle frompredefined angle settings between the connector and the markerarrangement, and (b) a detailed view of the individual components of thehinge joint.

FIG. 9 shows the example marker assembly from FIG. 8, where the magneticclamp mechanism is used instead of a spring.

FIG. 10 shows (a) an example marker assembly based on a hinge joint witha pin fixation which allows the user to select an angle from a set ofpredefined angles between the connector and the marker arrangement, and(b) a detailed view of the individual components of the hinge joint.

FIG. 11 shows (a) an example marker assembly based on a ball joint whichallows the user to select any angle between the longitudinal axis of themedical instrument and the marker arrangement, and (b) a detailed viewof the individual components of the ball joint.

FIG. 12 lists examples of open and closed ring shapes for the markerassembly.

FIG. 13 illustrates the two example types of medical instruments thatdiffer by their handling by the surgeon, showing (a) an instrument thatis twisted clockwise or counterclockwise by a small angle around itsshaft, and (b) an instrument that is fully rotated several times.

FIG. 14 shows (a) an example marker assembly with a clamp that has twoclaws, which allows a fixed connection between the shaft of the medicalinstrument and the marker arrangement, and (b) a detailed view of theindividual components of the clamping mechanism.

FIG. 15 shows the example marker assembly with a fixed connectionbetween the shaft of the medical instrument and the marker arrangementbased on a collet chuck adaptor, showing (a) the marker arrangement withthe spring collet and the nose piece, (b) the marker assembly attachedto the shaft of a medical instrument, and (c) a semi-transparent view ofthe attachment.

FIG. 16 shows (a) the example marker assembly attached to a rotatablemedical instrument, where (b) shows that full rotation of the medicalinstrument is possible while the marker assembly is held.

FIG. 17 shows (a) the example marker assembly attached to a rotatablemedical instrument, where only one stopper ring is used and (b) asemi-transparent view to show the position of the stopper ring insidethe handle.

FIG. 18 shows components of an example embodiment of a marker assemblythat allows the marker assembly to be removably attached to differentmedical instruments, showing (a) the marker assembly, (b) the connectionadapter which is attached to each tracked medical instrument, and (c) acalibration tool to ensure that the same distance between the connectionadapter and the tip of the medical instrument is obtained.

FIG. 19 shows detailed views of the marker assembly shown in FIG. 18,showing (a) an external view of the assembled marker assembly, (b) anexploded assembly view, and (c) a semi-transparent view showing theinternal components.

FIGS. 20(a) and (b) illustrate the placement of the connection adapteronto the medical instrument.

FIG. 21 illustrates the clamping of the marker assembly onto the medicalinstrument.

FIG. 22 illustrates the steps to secure the connection adapter on theshaft of the medical instrument using the calibration tool, including(a) placing the connection adapter inside the top bore of thecalibration tool, (b) inserting the shaft of the medical instrumentthrough the connection adapter, and (c) tightening the connectionadapter to the instrument shaft when the shaft tip touches the bottom ofthe calibration tool.

FIG. 23 illustrates an alternative example embodiment of the connectionadapter, which can be used for a fixed connection of the attachment tothe medical instrument, showing (a) a connection adapter with an outeraxial extension that is received in a corresponding groove with theinner sleeve, and (b) the compatibility of the inner sleeve with acylindrically symmetric connection adapter for rotatable instruments.

FIG. 24 shows components of an example embodiment of a marker assemblythat allows the marker assembly to be removably attached to differentmedical instruments, showing (a) the connection adapter which isattached to each tracked medical instrument, (b) the marker assemblywith mechanical clamping mechanism, and (c) a semi-transparent view ofthe marker assembly to show the clamping mechanism inside the handle.

FIG. 25 illustrates the mechanical clamping of the marker assembly fromFIG. 24 onto the medical instrument, showing (a) a solid view and (b) asemi-transparent view.

FIG. 26 shows a typical set of tracked medical tools that are usedduring medical procedures including (a) a pedicle finder, (b) awl, and(c)-(e) various taps, for which the instruments shown in (c) to (e) areconnectable to removably attachable marker assembly (O. In this example,the taps are used with the rotatable tracked attachment, while thepedicle finder and awl have a fixed attachment that is tracked.

FIG. 27 (a) shows a surgeon's hand holding the tracked tool with markerassembly in a suitable orientation for tracking. The marker assembly isat a suitable angulation from the rotatable tool shaft. (b) shows acut-away view of the tool shaft, showing one particular embodiment of aspring-locked rapid exchange system configured for use with multipletool tips. Example tool tip selections include (c) awl, (d) pediclefinder, (e) tap, and (f) variable length screws pre-mounted onscrewdriver bits. In the embodiment shown, the distance between the tiplocation and the marker assembly is constant for maintaining calibrationafter tool tip exchange.

FIG. 28 shows a spring-locked exchange mechanism based on a springcollet for rapid exchangeable tool. (a) During use, the spring colletclicks on the notch in the locking feature of the inserted toolextension. (b) For release, the outside cylinder is slid, spreading thespring collet with a coned notch.

DETAILED DESCRIPTION

Various embodiments and aspects of the disclosure will be described withreference to details discussed below. The following description anddrawings are illustrative of the disclosure and are not to be construedas limiting the disclosure. Numerous specific details are described toprovide a thorough understanding of various embodiments of the presentdisclosure. However, in certain instances, well-known or conventionaldetails are not described in order to provide a concise discussion ofembodiments of the present disclosure. It should be understood that theorder of the steps of the methods disclosed herein is immaterial so longas the methods remain operable. Moreover, two or more steps may beconducted simultaneously or in a different order than recited hereinunless otherwise specified.

As used herein, the phrase “medical instrument” refers to any type ofinstrument or tool, which is used during surgery, diagnosis or othermedical examinations or procedures and has a longitudinal axis. Thelongitudinal axis may be defined by a longitudinal shaft. Possibleexamples are surgical instruments such as awls, screwdrivers, pediclefinders, and cutters used for example in spinal surgeries. Furtherexamples are drills and other tools in dentistry, needles for biopsy,and applicators for thermal therapies (including radiofrequency (RF)ablation, cryoablation, laser induced thermal therapy (LIT), ormicrowave ablation). One example for a non-surgical tool is a pointingstylus in image-guided procedures. Other non-limiting examples ofsurgical instruments include a section tip, shunt passer, scalpel/knife,scissor, forceps, bipolar, hook, retractor, dissector, drill, kerrisonrongeur, osteotome, needle, (micovascular) micro Doppler probe,screwdriver, monopolar, cusa, dilators, probe/stylus, bone impactor,K-wire, taps, speculum, and curette.

As used herein, the term “tracking system” is any device that allows thedetection of the position and orientation of an object in threedimensions (3D). As a possible example, an optical tracking systemoperating with visual or infrared light may include stereo cameras todetect the positions of passive optical markers (e.g. reflectivespheres) and/or active optical markers (e.g. light emitting diodes(LEDs)). Other non-limiting examples of tracking systems includeelectromagnetic tracking systems and structured light tracking systems.

As used herein, the term “marker” refers to a locating indicator thatmay be affixed or otherwise connected to a handheld implement, patient,subject, instrument, tool, or other component of a surgical system orsurgical field, and which is detectable by a tracking system for usedetermining a position or location. A marker may be active or passive,and may be detectable using an optical detector. An example opticalpassive marker is a reflective sphere, or portion thereof, and anexample active optical marker is an LED. Another example of a marker isa glyph, which may contain sufficient spatial and/or geometricalco-planar features for determining a three-dimensional position andorientation. For example, a glyph marker may include at least threecorner features, where the three corner features define a plane.

As used herein, the term “marker plane” refers to the plane shared byone or more markers that are attached to a handheld implement, such thatthe tracking markers are suitable for determining a three-dimensionalposition and orientation of the handheld implement by the trackingsystem when the markers are secured to the handheld implement. Themarker plane may be defined at an angle relative to the shaft of themedical instrument.

As used herein, the term “overhead tracking system” refers to a trackingsystem that is located above an object to be tracked. An overheadtracking system may be directly overhead, substantially overhead, oroverhead and laterally displaced. In some embodiments, a line of sightvector between the object to be tracked (e.g. a trackable handheldimplement) and the tracking system is oriented at an angle of at least45 degrees relative to a horizontal plane.

FIG. 1 shows an illustration of an example of a surgical guidance systemfor tracking the intraoperative location and orientation of a medicalinstrument relative to patient anatomy during a spinal surgery. Patient10 is shown in the prone position, with spine 15 exposed. The examplesystem employs a combination of an optical tracking system and astructured light system.

The optical tracking subsystem is used to detect the position andorientation of medical instrument 40. In the example embodiment shown inFIG. 1(a), the optical tracking subsystem includes stereo cameras withintegrated infrared lighting 25 and attachment of highly reflectivemarkers 65 to medical instrument 40. Due to their high reflectivity toinfrared light, markers 65 can be easily localized in each image of thetwo cameras 25. These image positions are used to calculate the 3Dposition of each marker 65 by geometrical triangulation. Thetriangulation process can be performed by first calculating the centerof mass of each of the detected markers in both camera views of thestereo calibrated camera system. This yields a set of marker points inboth camera views from which the disparity between corresponding pointsin both views can then be calculated. This disparity along with the xand y pixel locations of each marker in one of the camera views can thenbe transformed into a 3D spatial coordinate (in a relevant coordinatesystem) using a perspective transformation. If at least three markers 65are rigidly attached to medical instrument 40, it is possible to computeits position and orientation (the six degrees of freedom—6-DOF). It isto be understood that in some embodiments, less than three markers maybe employed for position and location tracking. For example, a singlemarker may be provided for position and location tracking, provided thatthe single marker includes sufficient spatial structure and/or content.An example of such a single marker is a glyph including co-planarspatial features such as corner or edge features.

In the example illustrations provided herein, markers 65 for the opticaltracking system are shown as reflective spheres, which are commonly usedfor passive optical tracking. However, any other type of markers, ormarker attributes, can be used depending on the used tracking systemsuch as, but not limited to, active markers (i.e. LEDs, which do notrequire integration of additional lighting) and passive markers (e.g.glyphs, varying marker color, varying marker size, varying markershape).

The structured light imaging subsystem shown in the example embodimentis used to generate topology datasets with sub-millimeter accuracy. Itincludes at least one illumination device 30 and at least one camera 35.The illumination device(s) 30 project temporally and/or spatiallymodulated light onto the surface to be imaged, while the camera(s) 35capture images of the illuminated surface. This active illuminationenables robust and efficient identification of pixel correspondencesbetween calibrated camera-projector (a projector may be thought of as aninverse camera) or calibrated camera-camera system. The correspondence(disparity) data can then be transformed into real-space coordinate datain reference frame of the calibrated camera(s) 35 and/or projector(s) 30by geometrical triangulation. During surgery, the structured lightsystem is positioned such that 3D surface topology of the surgical site,such as bony surfaces of the exposed spine 15, is acquired and used tocreate a virtual representation of the exposed bone that is registeredto pre-operative data (e.g. CT, MRI, US, PET, etc.) for continualsurgical navigation.

In order to utilize the optical tracking data in conjunction with thestructured light data, a calibration procedure can be employed to alignthe coordinate system of the optical tracking system to that of thestructured light imaging system. If the relative position of the opticaltracking system and the structured light imaging system is fixed, thiscalibration may be performed by obtaining the position of at-least 3points for a calibration object from both systems, and align the pointsto obtain the calibration transform. Alternatively, the structured lightimaging device may include fiducial markers, which may be tracked by theoptical tracking system itself. In this configuration, thetransformation between the coordinate system of the optical trackingsystem and structured light imaging system is continuously updated.

The structured light datasets can be registered to preoperative 3D imagedata (e.g. computer tomography (CT) or magnetic resonance tomography(MRT) data) on the processing device 45 using methods described inpatent application (PCT/CA2011/050257, the Detailed Description andFigures of which are incorporated herein by reference). With thecalibration between the structured light and the optical system, thetracked position of the medical instrument 40 is projected into thepreoperative 3D image data. The result is presented to the surgeon as anoverlay 85 on the registered 3D image data on a display 55 or othervisualization devices.

As shown in FIG. 1(a), tracking unit 20 is positioned in an overheadorientation, above exposed spine 15. During a surgical procedure,medical instrument 40 may be oriented such that its shaft 70 is notaligned perpendicular to the view axis of tracking unit 20 (as shown inthe Figure). In such a situation, which involves direct, substantiallyoverhead viewing (e.g. into or above a surgical incision), theperformance of the tracking system, and the ability to track medicalinstrument 40, may suffer when the markers 65 are arranged with a markerplane that is parallel to the axis 70 of the instrument shaft.

This conventional arrangement of markers is shown in FIGS. 1(b) and1(c). FIG. 1(b) shows medical instrument 40 having handle 60 and shaft70, with markers 65 attached in a plane that is substantially parallelto the axis of shaft 70. In FIG. 1(b), the optical tracking cameras 25are oriented in a conventional side viewing geometry, which is suitablefor assessing the position and orientation of medical instrument 30 overa wide range of angular orientations. Such an approach is commonly usedin conventional tracking systems that do not require a direct view aboveand/or into the surgical incision 75.

As shown in FIG. 1(c), the conventional marker orientation isproblematic when employed with the overhead, direct viewing system,(e.g. the overhead system shown in FIG. 1(a)). In the scenarioillustrated in FIG. 1(c), in which cameras 25 are positioned abovesurgical incision 75, the conventional vertical plane marker arrangementleads to marker shadowing and/or occluding when medical instrument 40 isoriented near the vertical direction.

FIGS. 2(a) illustrates an embodiment of a surgical guidance systemincluding tracking system 20, processing unit 45 (which is connectableto display 55), and medical instrument 40 including markers 65 that areoriented in a plane that is not parallel to the axis of medicalinstrument. Such an arrangement enables line of sight tracking ofmarkers 65 over a wide range of angular orientations of medicalinstrument 40. Display 55 may be integrated with the system (forexample, integrated with processing unit 45 in a single device), or maybe an external device to which the processing unit 45 is externallyconnected. Furthermore, as described further below, the system need notnecessarily include medical instruments 40 with markers 65 permanentlyattached thereto, and may additionally or alternatively include a marker65 attachment assembly that is configured to be removably attachable toone or more medical instruments 40.

FIG. 2(b) provides an example embodiment showing relative positioning ofthe marker plane 85 and a longitudinal axis 70 of medical instrument 40.As can be seen in the Figure, markers 65 are provided in marker plane 85that is not parallel to the longitudinal axis of medical instrument 40(in the present example, the longitudinal axis is defined by shaft 70 ofmedical instrument 40). By orienting marker plane 85 such that it is anapproximately horizontal plane for at least one potential intraoperativeorientation of medical instrument 40, a direct line of sight may bemaintained between cameras 25 and markers 65 over a wide variety ofpossible orientations of medical instrument 40.

FIG. 3 illustrates one example implementation of a removable markerassembly 100 according to an embodiment of the disclosure, where markerassembly 100 is shown as being removably secured to shaft 130 of medicalinstrument 110, below handle 115. Marker assembly 100 includes a supportmember (140, 145) for supporting tracking markers 150, which are alignedin a plane defined by distal arc 145. In this example, instrument shaft130 is inserted through a hole in connector 120. Set screws 125 securemarker assembly 100 to shaft 130, preventing sliding and rotation of themarker assembly 100. Although connector 120 is shown provided as anintegral portion marker assembly 100, connector 120 may be provided as aseparate component that is slid, clamped, or otherwise secured to shaft130, and may be separately interfaced or connected to marker assembly100. Other example implementations of marker assembly 100 and connector120 are described in more detail below.

The marker plane, as defined by distal arc 145, is angled relative tolongitudinal axis 130, to enable line of sight detection of markers 150by an overhead optical tracking system, over a wide range of overheadline-of-sight view angles. In the example embodiment shown in FIG. 4,the marker plane, as defined by distal arc 145, is shown angled relativeto longitudinal axis 130 such that the marker plane is approximatelyhorizontal when medical instrument 110 is oriented at an angle relativeto the horizontal plane.

As shown in FIG. 4, distal arc 145 of marker assembly 100 is offset fromlongitudinal axis 130 by one or more proximal segments 140, whichtogether with one or more distal segments 145, form a ring shapedstructure. In some embodiments, proximal segments 140 may lie outside ofthe marker plane, as shown in the example provided in FIGS. 3 and 4. Insome embodiments, proximal segments 140 extend from instrument shaft 130along a direction that is approximately perpendicular to longitudinalaxis 155 (or beyond perpendicular). This allows a user to grip shaft 130beneath proximal segments 140, without proximal segments 140 contactingor pressing against the user's fingers. In other embodiments, one ormore proximal segments extending from connector 120 may lie within themarker plane.

The ring structure, with dual members 140, provides rigid structuralintegrity and resistant to external torque, thereby providing aresilient assembly. Furthermore, the ring structure defines a hole 170(shown in FIGS. 3 and 5) through which a surgeon or other user may lookwhen operating with medical instrument 110 (as shown in FIG. 4). As canbe seen in FIG. 5(a), which illustrates the view from the perspective ofthe surgeon, the ring shape allows the surgeon a clear view on thedistal tip 135 of the shaft 130 during the normal use of the medicalinstrument. The surgeon is therefore able to visibly check the incisionor touching point of the medical instrument. This is illustrated in asketch of the surgeon's view through the marker attachment in FIG. 5(b).The surgeon's dominant hand for implant insertion (175) holds the handleof the tool while the non-dominant hand (180) resting on the edge of thesurgical incision 75 aligns the tool shaft. A clear view on the distaltip 135 and the exposed spine 15 is obtained for the surgeon.

The angle between the instrument longitudinal axis 155 in FIG. 4 and themarker plane can vary for different attachment designs depending on thetype of medical instrument 110, and the range of insert angles of theinstrument into the body. In one embodiment, the relative angle betweenthe longitudinal axis and the marker plane may be determined as follows.A range of angles corresponding to typical use of the medical instrument110 is first determined The relative angle between the longitudinal axis155 and the marker plane is then selected such that when the medicalinstrument 110 is oriented at the midpoint of this angular range, themarker plane is approximately orthogonal to the expected view axis ofthe overhead tracking system. In embodiments in which the view axis isapproximately in the vertical direction (i.e. direct overhead viewing),then the marker plane is selected to be approximately horizontal.

For example, the angular range for inserting pedicle screws duringspinal surgery depends on the treatment area/level and is patient anddisease specific since various diseases induce different kinds of spinaldeformations. Surgical operation ergonomics dictate that typicalsurgical incisions occur directly in front of the principle surgeon,with both hands in a comfortable position. The operating room light andother assistive devices (e.g., tracking system, LCD display, etc.) aretypically maneuvered, by the surgeon's upper extremity, in an abductedand externally rotated position, along an arc that is approximately 120cm to 150 cm in radius from the surgical incision. The surgeon'soperative view has a surgical axis defined by his/her nasion and thecenter of the surgical incision. Accounting for potential obstruction bythe surgeon's head, the optical axis (for operating room light oroptical tracking system) can be located approximately 30° off thesurgical axis (see 90 in FIG. 2(a)). Given this geometricalconsideration, coupled with operative experience, a range fromapproximately 50° to 70° for the relative angle between the longitudinalaxis and the marker plane provides optimal tracking of the instrumentsused during pedicle screw placements.

It is to be understood that this angular range is provided as anexample, and that for other types of medical instruments, the suitableangular range may differ. The suitable angle range for a given medicalinstrument may be determined by considering the typical orientations ofthe medical instrument during use.

In the marker assembly shown in FIG. 4, the relative angle between thelongitudinal axis 155 of the medical instrument 110 and the marker planeis fixed. Further embodiments of the marker assembly allow the settingof various angles by the user. The following embodiments provide someexample implementations in which pivotable, tiltable, hinged and/orrotatable mechanisms are provided for varying the angular orientation ofmarket assembly 100.

In one embodiment shown in FIGS. 6(a) and (b), a hinge joint 200 isemployed to vary the angular orientation of marker assembly 100. Hingejoint 200 includes pivot member 202, which is integral with markerassembly 100, and which is received between support members 204 and 206,which are integral to connector 120. Fixation screw 208 is placedthrough hole 205 in support member 204 and hole 203 in pivot member 202,and is received in threaded hole 207 in support member 206, such thatsupport members 204 and 206 clamp pivot member 202 in place at aselected angle. This allows the user to select an arbitrary angle asshown in FIG. 7. After fixing the angle with the fixation screw 208, thetool may be calibrated before tracking.

Fixation screw 208 provides but one example of a locking mechanism thatmay be employed to lock the angle of the pivotable marker assembly 100.For example, in another embodiment, shown in FIG. 8, provides a hingejoint 210 that is pivotable among a series of pre-selected angularorientations. Pivot member 202 is supported between support members 204and 206 on support bar 212. Pivot member 202, which includes notchstructures 214, is biased by spring 216 towards corresponding notchstructures 218 on support member 204. The user can choose betweencertain pre-defined angle settings.

In another example embodiment shown in FIG. 9, two magnets 225 and 230are employed to provide a biasing mechanism for fixing marker assembly100 at the selected angle. As a further modification of this embodiment,one of the two magnets 225 or 230 could be replaced by a magnetizablematerial.

In another embodiment shown in FIG. 10, a hinge joint 230 includeslocking pin 240 for fixation of pivotable marker assembly 100 in one ofseveral possible angular orientations. A shown in FIG. 10(b), fixationscrew 210 is employed to support pivot member 202 between supportmembers 204 and 206. Unlike the embodiment shown in FIG. 6, however,pivot member is held in a fixed orientation by the placement of lockingpin 240 with holes 232, 234 and 236 in support member 204, pivot member202, and support member 206, respectively. Pivot member 202 includes aplurality of such holes, such that the angular orientation of markerassembly 100 may be varied without detaching marker assembly 100 fromconnector 120.

In the embodiment shown in FIG. 11, a ball joint 250 is employed topivotally secure marker arrangement 100 to connector 120. Ball joint 250includes convex hemispherical member 252, which is attached to, orintegral with, marker assembly 100, and which is received in concavehemispherical portion 252, that is attached to, or integral with,connector 120. A fixation screw 256 is received in threaded hole 258within concave hemispherical portion 254 for securing ball joint 250 ina given angular orientation. Ball joint 250 allows the user to select anarbitrary angle between the longitudinal axis 155 of the medicalinstrument 110 and the marker plane.

When the aforementioned embodiments with a variable angular orientationof marker assembly 100 are attached to a medical instrument and employedwith a guidance system, it will generally be necessary to eithercalibrate the medical instrument or to select the calibration resultfrom a list of previously performed calibrations prior to initiatingtool tracking. Common methods of performing calibration include, but isnot limited to inserting the tip of the tool 135 into multiple landmarksof a calibration block with known (calibrated) geometry, and pivotcalibration, where the tool tip 135 is fixed in space, while the axis ofthe tool 155 is pivoted about the tip 135. Both these methods allow thetip 135 and axis 155 of the tool to be defined in terms of the markers150. However, in some of the aforementioned embodiments in which afinite number of fixed angular orientations are available, it maypossible to calibrate one of the many selectable angular orientations,and to employ the known angular relationship among the different angularorientations to calibrate any of the other angular orientations.

The ring shape of marker assembly 100, shown in FIG. 3 with a round arc,is but one non-limiting example implementation of many possible shapesfor marker assembly 100. FIG. 12 illustrates additional non-limitingexample shapes and configurations with an open or closed ring shape. Forexample, FIG. 12(a) shows a schematic of the round arc-shaped examplemarker assembly extending from connector 120. Other design examples arebased on (b) a full circle shape, (c) a rectangular shape, (d) atriangular shape, and (e) a hexagonal polygonal shape. In otherembodiments, marker assembly 100 may include an open gap, as shown inFIG. 12(f), and/or have arms on each side with dissimilar shapes and/orlengths, as shown in FIG. 12(g).

Embodiments of the marker assembly may be configured for attachment todifferent types of medical tools. Two example types of medicalinstruments with longitudinal shafts are shown in FIG. 13, in which theillustrated medical instruments differ according to their handling bythe surgeon. FIG. 13(a) shows a first example instrument type, such asan awl or a pedicle finder 110, which are typically rotated, relative tothe longitudinal axis of shaft 130, clockwise or counterclockwise 300 byless than approximately 180°. For such instruments 110, a fixedconnection may be made between the instrument shaft and the markerassembly 100. As a consequence, the marker assembly 100 is rotated inunison with the medical instruments 110 around the shaft 130. If therotation angle does not exceed 180°, the surgeon does not interrupt theability of the optical tracking system to maintain line of sightvisibility, and therefore, the tracking ability to track the instrumentis maintained.

One example of a fixed connection is the insertion of the instrumentshaft 130 through a hole in a connector block 120 and fixation of thearrangement with set-screws 125, such as in FIG. 3. Another fixedconnector with a marker arrangement 100 is a clamp 260 with two claws265, which attaches to the longitudinal shaft 130 of the medicalinstrument 110 as shown in FIG. 14. An additional fixation screw 270could be used to squeeze the two claws 265 and thereby secure theconnector tighter onto the instrument shaft 130.

Another fixed connector with a marker arrangement 100 is a collet chuckadaptor as shown in FIG. 15. A spring collet 275 is fixed to, orintegral with, marker assembly 100. After inserting shaft 130 of medicalinstrument 110, nose piece 280 fastens the spring collet 275, and thusmarker assmeblyl00, to shaft 130.

A second type of medical instrument is shown in FIG. 13(b), whichincludes, for example, screwdrivers and taps 400. These instruments arenormally rotated several times in the same direction 305 around thelongitudinal axis of the instrument shaft 405. For such instruments, themarker assembly may include a connection that allows a free rotation ofthe instrument shaft relative to marker assembly 100. For example, asdescribed further below, the marker assembly and connector may include aportion that is clasped by the surgeon with one hand, providing supportand enabling the surgeon to maintain the visibility of the markerassembly by the tracking system. This ensures that the surgeon does notblock the line of sight of the tracking system on the tracking markersduring rotation of the medical instrument 400. Accordingly, unintendedblocking of line of sight on the markers by the arms of the surgeon isavoided, maintaining the ability to track the medical instrument 400during use.

One example embodiment of such a connector is shown in FIG. 16(a), whichincludes a pivotable marker assembly 410 with an inner hole that issufficiently large to accommodate the outer diameter of shaft 405 ofmedical instrument 400. Stopper rings 415 and 425 (optionally securedwith fasteners such as set-screws), or other structures along theinstrument shaft, fix or limit the relative position of the pivotablemarker assembly 410 along instrument shaft 405. As illustrated in FIG.16(b), during surgical use, the surgeon clasps the elongate cylindricalportion 420 of pivotable marker assembly 410 with one hand, while theother hand can be used to rotate medical tool 400 by grasping handle430.

It should be recognized that variations and modifications of themechanism for connection between the marker assembly 410 and shaft 405of the medical instrument 400 may be implemented. For example, one ring445 can be integrated into the pivotable cylindrical portion 435 of themarker assembly 410 as shown in FIG. 17. The ring 445 is secured withfasteners such as set-screws (using the hole 440) and fix of thepivotable marker assembly 410 along shaft 405 of the medical instrument400.

Many commercially available tracking systems are compatible with limitedarrangements of markers on tracking attachments. For example, opticaltracking systems that employ passive spherical optical markers typicallyrequire a minimal distance between markers and specific variations inthe distances between marker pairs in order to track multipleinstruments. As a consequence, the relative spacing of the markersbecomes larger with the number of tracked instruments when eachinstrument is tracked with an individual marker arrangement.Unfortunately, larger marker attachments make it more difficult and lessconvenient for the surgeon to handle the medical instruments.

In one embodiment, a connection adapter is attached to, or provided aspart of, the medical instrument itself (for example, permanently affixedto the shaft, or formed as a monolithic component of the shaft), suchthat the connection adapter is configured to mate with, or otherwiseconnect to, the removably attachable marker assembly. Multipleconnection adapters, each having a common outer cross-section(cross-sectional profile), may be provided, for attachment to multiplemedical instruments. Such an embodiment enables one marker assembly tobe used for a plurality of different medical instruments, even if theshaft diameter, or shaft length, differs among the medical instruments.

Accordingly, in one example embodiment, which may be employed to reducethe number of marker assemblies needed for tracking of multiple medicalinstruments, a connection adaptor is integrated with, or attached to,one or more medical instruments to be tracked, where the connectorallows the coupling and removal of one marker assembly to multiplemedical instruments. In some embodiments, the coupling mechanism maysupport the repeated coupling and decoupling of the marker assembly tomultiple medical instruments without the need for recalibration.

FIGS. 18-21 illustrate an example embodiment of a removably attachablemarker assembly in which magnetic clamping is employed to secure anattachment assembly to a connection adapted attached to the shaft of amedical instrument. A first component is marker assembly 500, whichincludes handle 505 and marker support 510. During use, handle 505 isheld by the surgeon with one hand, as described in the previous section.Handle 505 includes bore 515 extending below the top of the device.

Connection adapter 520 is a cylinder formed, at least in part, from amagnetic material, such as a diamagnetic, paramagnetic, or ferromagneticmaterial. In one example embodiment, connection adapter 520 may beformed from magnetic steel. Connection adapter 520 is placed around andsecured to the shaft of the medical instrument. Connection adapter 520may then be rotatably received within bore 515 within handle 505 inorder to indirectly couple marker assembly 510 to the medicalinstrument. As further described below, an integrated magnet withinhandle 505 secures magnetic connection adapter 520 via an attractivemagnetic force, thereby removably attaching marker assembly 510 to themedical instrument. An additional calibration tool 600, described infurther detail in FIG. 22, allows the positioning of connection adapter520 at a well-defined distance along the shaft from the tip of themedical instrument, allowing exchanging of marker assembly 500 amongmultiple pre-calibrated medical instruments without the need forintraoperative re-calibration.

FIG. 19 illustrates an example implementation of the internal componentsof marker assembly 500 (shown in from an external perspective in FIG.19(a)). In FIG. 19(b), an exploded view of the internal assembly isprovided, showing internal sleeve 525, which is also formed from amagnetic material and includes providing inner bore 515 for receivingconnection adaptor 520. Ring magnet 530 is supported below counter piece525 above end cap 535. Ring magnet 530 has an outside-diameter largerthan the diameter of bore 515, and an inside diameter that is largerthan the diameter of the largest shaft associated with the medicalinstruments to which the marker assembly is to be removably attached. Asemi-transparent view through assembled marker assembly 500 isillustrated in FIG. 19(c), showing the position of internal sleeve 525,ring magnet 530 and fixation end cap 535 inside handle 505.

The operation of rotatable marker assembly 500 is described as follows.For each medical instrument 400 in a set of instruments to be trackedduring surgery, a connection adapter 520 is provided and secured to theinstrument shaft (as shown in FIG. 20). Each connection adapter 520 hasan inside bore configured to receive the shaft 405 of its correspondingmedical instrument 400. As shown in FIG. 20(a), the connection adapter520 is slid along the shaft 405 of the medical instrument 400.Connection adapter 520 is then fixed with set-screws 540 at the desiredposition on the instrument shaft 405 as seen in FIG. 20(b).

Marker assembly 500 is then slid over connection adapter 520 anddetachably secured in place, as shown in FIGS. 21(a) and 12(b). To clampmedical instrument 400 to marker assembly 500, the instrument shaft 405and connection adapter 520 are inserted through the bore 515 of withininternal sleeve 525. As shown in the semi-transparent view of FIG.21(b), connection adapter 520 is directly clamped to ring magnet 525inside marker assembly 500. If the position of connection adapter 520 isnot changed, the relationship between marker assembly 500 and themedical instrument 400 is well-defined and reproducible as required forthe tracking of the instrument. Marker assembly 500 thereby enables thetracking of the trajectory of the instrument shaft 405 via an overheadoptical tracking system.

This approach is efficient to track medical instrument 400 after thecalibration, using the calibration procedures of the specific trackingsystem. The approach can also be used to track the trajectory ofmultiple instruments using the same marker attachment.

However, if tracking of the trajectory and the tip multiple medicalinstruments is desired, the position of connection adapter 500 on theshaft 405 of each medical instrument 400 may be calibrated such that thedistance between the connection adapter 520 and the tip of each medicalinstrument is substantially equal.

This may be achieved, in one example embodiment, using a calibrationtool. For example, calibration tool 600, shown in FIG. 18(c), may beemployed to connect the connection adapter 520 to the shaft 405 of themedical instrument 400, as demonstrated in FIG. 22. Connection adapter520 is initially placed into the top hole 605 of calibration tool 600,and is inserted until its motion is impeded by stop 610, which is alocation at which the inner diameter of calibration tool 600 decreasesfrom the outer diameter of connection adapter 520 to a smaller diameter,which is larger than the diameter of the largest shaft used in a medicalinstrument set. Accordingly, after the connection adapter 520 is fullyslid into the hole 605, it is located with a well-defined distancerelative to the bottom 615 of calibration tool 600.

Shaft 405 of the medical instrument 400 is then inserted though the bore545 in connection adapter 520, until the tip of the instrument shaft 405encounters the bottom 615 of calibration tool 600. Afterwards, as shownin FIG. 22(c), set-screws 540 of connection adapter 520 are tightened,thereby securing connection adapter 520 to the medical tool 400. Usingthis approach ensures that connection adapter 520 is always positionedin the same distance from the shaft tip of the medical instrument 400,and therefore, a re-calibration of the medical instrument 400 is notnecessary.

The aforementioned devices and methods allow tracking of multiplemedical instruments with one attachment (or a plurality of attachments,if so desired), provided that connection adapter 520 of each instrumentis initially placed at a pre-calibrated location. This may be achieved,for example, using calibration tool 600 and following the procedure asshown in FIG. 21. In addition, no re-calibration is necessary for futureuses of the tool (e.g. for the next surgery), provided that theconnection adapters are either left on the medical instruments orremoved and replaced using the calibration tool.

While the aforementioned embodiments provided rotatable markerattachments, a locking mechanism may be employed to a furthermodification of the above embodiment to prevent the rotation of certainmedical instruments inside the attachment. An example implementation ofthis embodiment is shown in FIG. 23(a). Connection adapter 550 has anon-cylindrically symmetric feature for locking an orientation of themedical instrument within the bore of the internal sleeve 560. Forexample, as shown in the Figure, the non-symmetric feature may be a lineof increased thickness 555 of the surface of connection adapter 550, onthe outside surface, parallel to the cylinder axis, which is axiallyreceived in corresponding grooves 565 within internal sleeve 560. Thisembodiment also accommodates the previously described rotatableconnection adapter 520, as shown in FIG. 23(b), because groove 565 ininternal sleeve 560 does not impede rotation of connection adapter 520.Accordingly, the presence of such non-cylindrically symmetric featureson a given connection adapter determines whether or not thecorresponding medical instrument has a fixed or a rotatable connectionto its marker assembly.

Another embodiment, shown in FIG. 24, employs mechanical clampinginstead of the magnetic clamping to removably attach the marker assemblyto the shaft 405 of the medical instrument 400. For example, as shown inthe Figure, connection adapter 700 (which may be a metallic cylinder)can include a groove 705 for receiving a clamping fastener. Connectionadapter 700 is placed and secured to the shaft 405 of the medicalinstrument 400, in a manner similar to the procedure descripted in FIG.20. An additional calibration tool can be used to position theconnection adapter 700 at a well-defined distance along the shaft fromthe tip 450 of the medical instrument 400, in a manner similar to theprocedure shown in FIG. 22.

Marker assembly 710 has an insert hole 715 with the same diameter as theoutside diameter of the connection adapter 700. Inside marker assembly710 is a sliding plate 720 with a hole with the same diameter as theconnector adaptor 700, as can be seen in FIG. 24(c). Two springs 730hold this sliding plate 720 in a default position, shown in FIG. 24(c),in which axis of hole 725 is slightly off-centered relative to axis ofhole 715 of marker assembly 710.

FIG. 25 illustrates the process of clamping connection adapter 700within marker assembly 710, where connection adapter 700 is secured toshaft 405 of medical instrument 400. In order for marker assembly 710 tobe able to receive connection adapter 700 in an unobstructed fashionwithin hole 715, the user presses sliding plate 720, thereby compressingsprings 730 to align the axis of hole 725 with the axis of hole 715.After aligning the hole axes, connection adaptor 700 may be fullyinserted into hole 715 of marker assembly 710. The user may then releasesliding plate 720 to its default position, such that a proximal portionof sliding plate 720 engages groove 705 and secures the axial positionof marker assembly 710.

The example clamping mechanism illustrated in FIGS. 24 and 25 issuitable for use with medical instruments which involve rotation duringuse. If it is preferable that a medical instrument should not berotatable inside the attachment, a grove in a manner similar to oneshown in FIG. 23 can be added to the device. It is also to be understoodthat the embodiment shown in FIGS. 24 and 25 is merely one exampleembodiment of a mechanical clamping mechanism, and that a wide range ofother mechanical clamping mechanisms may be alternatively oradditionally employed. For example, other detent mechanisms and/orfasteners (such as set screws) may be employed for mechanical clamping,with or without allowing rotation of connection adapter 700 within hole715 of marker assembly 710. In other example implementations, the markerassembly may be removably secured to the shaft a suitable engagementmechanism such as mating threads or other interlocking features and/orsecuring the marker assembly using a friction fit.

The above embodiments can be combined to track an entire set ofdifferent medical instruments, for example, during surgery. One exampleis the set of medical instruments used during pedicle screw placement inspine surgery, shown in FIG. 26. This set can include an awl 800, acutter 810, taps of different sizes 830 and 840, and screwdrivers 850.Since the awl 800 and the cutter 810 are normally twisted back and forthby a smaller rotation angle, two attachment designs with fixedconnectors are used (FIGS. 15 (a) and (b)), which have differentarrangements of markers (805 and 815) for instrument identification.

In this example, reflective spheres are used as markers for an opticaltracking system. To reduce the impact of the marker attachment on thesurgeon, a round-arc shape of the marker support is used. In addition,the attachments of the awl 800 and cutter 810 have the same dimensions,use a set of markers with a slightly different geometric arrangement,and are chosen to be as small as possible to reduce overall weight andvisual impact on the surgical field of view.

In the present example embodiment, the surgeon may change markerassemblies between varying sizes of taps 830 and 840 and the screwdriver850 quite frequently during the surgery. These instruments are alsonormally rotated several times around the instrument shaft. For theseinstruments the previously described exchangeable attachment device witha rotatable connection 500 is preferred. As can be seen in FIG. 26, eachof these instruments is connected to a corresponding connection adapter835, 845 and 855. The connection adapters in this illustration areplaced with the calibration tool and have therefore the same distance tothe tip of each respective instrument shaft.

Alternatively, in some situations, it is not necessary during navigatedprocedures for the surgeons to know the tip location of their tool forimage guidance—the tool trajectory alone is sufficient. Therefore othermedical tools, whose tip location has not been calibrated to theadaptor, can still be used for navigation, provided that the adaptorfits snugly around the bore of the tool such that the axis of the toolis aligned to the intended axis (trajectory) of the adaptor.

As mentioned above, for some marker types, the relative spacing of themarkers becomes larger with the number of simultaneously trackedinstruments. Two types of attachments have been described, one of whichis specifically designed to fit one tool 100, and the other is anexchangeable attachment 500 that can be attached to multiple tools. Inone example application, given the complete set of tools available tothe surgeon, the exchangeable attachment may employ a marker arrangementwhere the spacing of the markers is large compared to the non-swappablemarker attachment.

Such an embodiment may be useful when the exchangeable attachment isheld relatively stationary by the surgeon, and only the tool itself isrotated, such that the arc of motion (sweep area) of the exchangeableattachment is small. Therefore, the marker support 510 can be relativelylarge, whereas for the non-swappable marker attachment, a large markersupport would sweep out a much larger area when performing clockwise andanti-clockwise rotations, and would therefore be more obstructive.Furthermore, since the exchangeable attachment is held by the surgeon'shand, as shown in FIG. 16(b), the hand can obstruct part of thesurgeon's view of field through the marker support. Therefore it may beuseful to have a marker support with a larger opening for theexchangeable attachment.

Referring now to FIG. 27, an embodiment is illustrated in which a markerassembly 900 is attached to a rapid exchange handheld tool body 910, andwhere the shaft of the tool body 910 is configured for use with aplurality of exchangeable tool extensions, such as bits and/orfasteners. As shown in the Figure, a marker assembly 900 is secured(permanently or removably) to the rapid exchange tool 910. The markerassembly 900 may be provided according to any of the precedingembodiments.

The Figure illustrates an embodiment in which a spring-locked exchangemechanism 920 is employed for rapid exchange of a bit, fastener,combination thereof, or other exchangeable tool extension or combinationthereof. For example, when employed with awl 940, a proximal portion 942of the shaft of awl 940 is received within longitudinal bore 925 ofshaft 930, and is secured in place by the spring-locked mechanism 920.Referring to FIG. 27(b) and (c), the proximal portion 942 of awl 940includes locking features 944 that cooperate with corresponding featuresin spring-locked mechanism 920.

As shown in FIG. 28, the connector for the spring-locked exchangemechanism could be based on spring collet 920. The spring collet 920clicks on the notch in the locking feature 944, when a tool extension940, 950, 960, 970, or 980 is inserted into the rapid exchange tool 910as shown in FIG. 28(a). The spring collet 920 is covered by a cylinder930 which has a coned notch 995 in the inside pointing towards thespring collet 920. If the cylinder 930 is pressed towards the rapidexchangeable tool 910 as shown in FIG. 28(b), the coned notch 995spreads the spring collet 920 and releases the tool extension 940, 950,960, or 980. Afterwards another tool extension can be inserted into therapid exchange tool 910.It is to be understood that the spring-lockedmechanism illustrated in FIG. 27 is but one example implementation of amechanism for removably securing a bit, fastener, or other functionalelement to rapid exchange tool 910. Other suitable and exampleimplementations/mechanisms include thread-lock, magnetic, or pneumaticmechanisms. In one embodiment, mechanical contact between the outershaft of the distal functional element and the inner bore 925 of shaft930 and utilizes compression and static friction. Other embodiments mayinclude thread-lock, clip-lock, or pneumatic lock techniques.

According to one embodiment, the rapid exchange device described abovemay be employed for tracking fasteners of variable lengths, such asimplantable screws 965 and 975 in FIG. 27(f). In one embodiment, screws965 and 975 may be pre-mounted on screwdriver tips 970 and 980 , wherethe lengths of screwdriver tips 970 and 980 are provided such that thetip locations 990 of the screws remain invariant relative to theposition of marker assembly 900, thus preserving the calibration oflocation 990 under exchange of the different screwdriver and screwassemblies. This embodiment thus allows for tracking of the tip locationof an exchangeable tool extension that includes a tool extension member(such as a screwdriver extension) and a functional member (such as ascrew) removably attached to the tool extension member, where calibratedtracking may be maintained without the need for further calibrationdespite the use of functional members having different lengths.

FIGS. 27(c)-(e) illustrate other examples of exchangeable distalfunctional elements, include awl 940, pedicle finder 950, tap 960, withthe location of the tip being invariant with respect to the markerassembly 900.

In other embodiments, the relative location between the tip 990 of theinstalled functional extension need not be fixed relative to thelocation of marker assembly 900, provided that the relative location isprovided to the tracking system. For example, the tracking system may bepre-programmed with the relative locations of the distal tip of variousexchangeable tool extensions, such that when a rapid exchange procedureis performed and a first exchangeable tool extension is removed andreplaced with a second exchangeable tool extension, the system canselect the appropriate calibration data for the second exchangeable toolextension from the pre-programmed calibration data.

The aforementioned marker assemblies and related devices may be employedfor tracking medical instruments, for example, for computer-aidednavigation of, or for, various medical methods and procedures. Asmentioned above, many medical instruments, such as awls, cutters,screwdrivers or drills can be tracked using the aforementioned markerassemblies. This allows the use of navigation of, or to support, varioussurgeries including for example spine, hip, knee, and brain surgeries,where a direct view on the corresponding bone surface is possible. It isto be understood that the aforementioned examples may be for a widevariety of medical applications beyond surgery, such as guidance duringthe positioning of applicators for thermal therapies or navigation ofbiopsy needles.

Although the preceding embodiments have been described as exampleimplementations involving medical applications, it is to be understoodthat the marker assemblies described above may be employed for thetracking of any handheld implement. Examples of other trackable handheldimplements include tools and video game controllers, such as those thathave a longitudinal shaft, longitudinal body, longitudinal member, orlongitudinal axis.

For example, in one embodiment, the devices, systems and methodsdisclosed above can be adapted for the tracking of a video/computer gamecontroller or handpiece. In one example implementation, a video gamecontroller tracking system could be mounted on the ceiling above a groupof players, who use tracked controllers such as styluses or othercontrollers to interact with different elements of the game. Theceiling-mounted tracking system would enable the tracking, withoutobstruction, of all the players' controllers. In another exampleembodiment, the tracking system could be integrated with a monitor, suchthat during gameplay, a player points a tracked stylus at the trackingsystem in order to interact with the virtual components of the game (forexample a hunting simulator).

In another example implementation, the tracked stylus could also be usedin combination with a monitor, computer, and tracking cameras to be useda rehabilitation device, where the user would be asked to perform a setof spatial tasks such as connecting virtual dots or tracing out virtualobjects projected onto the monitor showing the user, the virtual objectsand their environment. This rehabilitation system could be used to trackthe progression/regression of patients with uncontrollable movement suchas Parkinson's disease based on their interaction with the system as afunction of time.

Therefore what is claimed is:
 1. A marker assembly for locating ahandheld implement, said marker assembly comprising: a support memberconnected or connectable to a longitudinal portion of the handheldimplement, said support member comprising: a pair of proximal segmentsconfigured to extend from said longitudinal portion when said supportmember is connected to the handheld implement; and at least one distalsegment extending from said proximal segments; wherein said proximalsegments and said at least one distal segment at least partiallysurround a central aperture; wherein said pair of proximal segments forma proximal plane and said one or more distal segments form a distalmarker plane, wherein said distal marker plane is angled, relative tosaid proximal plane, toward a distal region of said handheld implement;and one or more tracking markers affixed to said distal segment; whereinsaid one or more tracking markers are suitable for locating athree-dimensional position and orientation of the handheld implementwhen said marker assembly is secured to the handheld implement; whereinsaid proximal segments and said at least one distal segment form saidcentral aperture such that, when said marker assembly is secured to saidhandheld implement and during use of said handheld implement, anunobstructed view of a distal end of the longitudinal portion isprovided through the aperture.
 2. The marker assembly according to claim1 wherein said at least one distal segment is a single distal segmentconnected to each proximal segment of said pair of proximal segments. 3.The marker assembly according to claim 1 wherein said distal markerplane is oriented at an angle between 50 and 70 degrees relative to thelongitudinal axis.
 4. The marker assembly according to claim 1 whereinsaid distal segment is shaped in an arc.
 5. The marker assemblyaccording to claim 1 wherein said pair of proximal segments and said atleast one distal segment are configured such that said central apertureis sufficiently large to permit viewing of at least two spinal levelswhen a distal portion of the handheld implement is contacted with thespine and said central aperture is viewed by a user from a viewinglocation behind the handheld implement and said marker assembly.
 6. Themarker assembly according to claim 1 wherein said pair of proximalsegments and said at least one distal segment shaped to form a closedring or an open ring.
 7. The marker assembly according to claim 1further comprising a connector for connecting said marker assembly tothe handheld implement.
 8. The marker assembly according to claim 7wherein said connector is configured to be gripped by a hand.
 9. Themarker assembly according to claim 7 wherein said connector isconfigured to allow free rotation of the handheld implement relative tosaid connector.
 10. The marker assembly according to claim 1 furthercomprising a mechanism for varying an angle of said distal marker planerelative to the longitudinal axis when the marker assembly is connectedto the handheld implement.
 11. The marker assembly according to claim 10wherein said mechanism is configured for locking an orientation of saiddistal marker plane in one or more pre-selected angles.
 12. A system fortracking a handheld implement during a medical procedure, said systemcomprising: a marker assembly according to claim 1, wherein said markerassembly is connected to said handheld implement; an overhead opticaltracking system comprising at least two cameras, wherein the opticaltracking system is configured to detect a signal associated with eachtracking marker of said marker assembly; and a processor configured toreceive said signals and to calculate a relative position andorientation of said handheld implement based on said signals.
 13. Thesystem according to claim 12 wherein said handheld implement hasassociated therewith a pre-defined range of angular orientationsrelative to the patient during the medical procedure; wherein saidmarker plane is angled relative to the longitudinal axis such that whensaid handheld implement is positioned at a mid-point of the pre-definedrange of angular orientations, a view axis of said overhead trackingsystem is approximately orthogonal to said marker plane, such that saidone or more tracking markers are suitable for locating thethree-dimensional position and orientation of said handheld implementwhen said handheld implement is oriented within the pre-defined range ofangular orientations.
 14. The system according to claim 12 wherein thetracking system is an overhead optical tracking system comprising twocameras, wherein the optical tracking system is configured to detect anoptical signal associated with each tracking marker of said markerassembly.